Buttress pins are implants that are used for fixation of fractured bones. The buttress pin has a base which is usually ‘U’ shaped and the pin is fixed to the stable bone fragment with a bone screw and washer. At the opposite end, the buttress pin has two legs that extend out of the plane of the base of the implant. These legs are often used to penetrate an unstable bone fragment, allowing it to be manipulated into appropriate position much like a joystick. Once the fragment is manipulated into position, the base of the implant is secured proximally with the bone screw and washer. These implants have been described in my previous patents U.S. Pat. Nos. 5,709,682 and 6,113,603. Currently, however, buttress pins are only made with the legs separated at a fixed distance throughout the length of the buttress pin. In addition, existing buttress pin designs all have both legs penetrating the distal fragment in a position located at an equal distance from the ‘U’ shaped bend at the base of the buttress pin.
In some circumstances, such as fixation of the volar surface of the radius, the straight ‘U’ shaped buttress pin design with the legs spaced at an equal distance from the ‘U’ shaped bend is not the ideal configuration since this bone is wider distally than it is proximally. Hence, a buttress pin configuration having a separation of the legs that is wide enough to spread the support out in the distal fragment creates the situation that the implant (or pair of implants if two are used) is too wide to fit proximally. If the leg spacing is narrowed to allow one or two side by side implants proximally, the spread of the fixation legs distally is not wide enough and is inadequate for good fixation of the unstable, distal fragment. In addition, since the articular surface of the bone is not perpendicular to the long axis of the bone shaft but is at an angle or inclination, one leg of the buttress pin is often either too far distally or not far enough. Moreover, attempting to bend the pin to accommodate these deficiencies often results in changing the axis of the leg into a divergent position, compromising fixation.
Fixation of these buttress pins to the bone to reduce the fracture also poses a number of problems.
Surgeons may have to manipulate two wire implants into position while holding a small fragment, and at the same time drill and measure a hole and then place a screw and washer over the implant to secure it to the bone. In addition, since most buttress pins have two legs that extend from its ‘U’ shaped base, the surgeon is limited to two points of fixation for each wire implant used.
Another major technical difficulty in placement of wire forms buttress pins is to keep the washer from spinning around during insertion of the bone screw. Most washers have projecting tabs or lugs on each side thereof to capture the wire. However, these tabs spin over the wire and make it extremely awkward and time-consuming to correct the position of the washer.
Another limitation of buttress pins in general that are used to buttress curved articular fragments is that the legs of the buttress pin (or the posts of a buttress plate) that are used to buttress the articular fragment are, for the most part linear and predominantly oriented along a single axis. Since the articular surface is curved and the legs of the buttressing element are predominantly straight, there is only a single point of contact between the apex of the subchondral bone of the curved articular surface with the nearly straight leg of the buttressing element. In some cases, the buttressing element is nearly perpendicular to the long axis of the bone shaft whereby the curved articular surface has little stability to dorsal or volar migration. If, on the other hand, the buttressing element is inclined dorsally or volarly, a free articular fragment will tend to migrate along the path of least resistance to the side volarly or dorsally where there is no support.
Furthermore, plates that provide buttressing elements which are oriented at different angles are forced to fix the relative position of the multiple buttressing elements or posts to fixed locations as they enter the plate. However, since the individual osseous anatomy may be variable, the optimal relative location of two or more buttressing elements may differ from case to case. In this situation, buttress plates in which the entry locations of the posts or pegs through the plate are fixed to a specific relative location to one another cannot compensate for variations in bone morphology.